The invention relates to an apparatus for storing and reproducing electric signals to be analysed. The apparatus comprises a vacuum tube provided with an electron gun for emitting an electron beam which is subjected to the influence of the electric signals to an analysed and which is controlled by a beam focusing and deflection system for writing the trace of the electric signals to be analysed on the sensitive areas of two matrices of charge transfer devices in the form of stored charges. Electric signals corresponding to the stored charges are derived from the tube by means of read registers; these signals are processed in processing circuits and then displayed in the form of electric signals reproduced on a display screen.
An apparatus of this type is known from the Soviet document SU No. 1150677. This known apparatus comprises an electron source, an electron beam focussing and deflection system and a target formed by two matrices of charge transfer devices (CTDs). The electron beam whose current is modulated in accordance with an input signal to be analysed is directed towards one or other of the CTDs by a selection device. The two CTDs are superposed so that the boundary which separates them is parallel to the horizontal direction of scanning effected by a time base. The electron beam which is modulated in intensity by the signal can thus write its information in each CTD on the sensitive regions constituted by two or three rows of CTDs located on either side of this boundary. The charge quantity at each point in this region of 2 or 3 rows is thus representative of the signal to be analysed. Although the electron beam is focussed, the beam spot is sufficiently large to write on 2 or 3 rows at a time, on one of the CTDs when scanning in one direction, termed tracing, and on the other of the CTDs when scanning in the opposite direction, termed retracing; the tracing and retracing being continuous. When the charges are stored in the 2 or 3 rows, they are transferred and added in accordance with the columns of the CTD to an output register with the aid of different clock pulses. The registers of each CTD operate alternately in opposite senses corresponding to their inscription for depleting their charges to an output amplifier which is connected to a processing and display circuit.
This prior art apparatus has for its object to enhance the conversion precision of the signal to be analysed, to increase the volume of the registered signals and to realise an uninterrupted conversion at a writing speed which is slower than the transfer speed of the charges by the output registers.
This device can be used in automatic control and data display systems or in oscillograph systems, but it does not have an operating speed which is fast enough for modern oscilloscopes.
Furthermore it does not provide the possibility of effecting pre-triggering, which is very useful and appreciated by users of oscilloscopes. Pre-triggering consists of the following. For obtaining a stable image on the screen, the time base in an oscilloscope is triggered by the signal to be observed in accordance with thresholds which can be modified. This signal must thus have a sufficient level for effecting this triggering. The events in the signals which are produced just before the triggering instant are thus lost. Particularly when the signal is a non-recurrent signal, one part of the information contained in the signal cannot be observed. Pre-triggering thus consists of preserving in the memory samples which precede and succeed, in time, the triggering instant. Thus, ultimately it is only possible to reproduce the form of the signal thus memorised on a display screen.
This prior art device does not provide a solution for storing in accordance with pre-triggering.